Vapor generator wall construction



Oct. 5, 1965 J. COOPER ETAL 3,209,734

VAPOR GENERATOR WALL CONSTRUCTION Filed March 50, 1962 4 Sheets-Sheet 1 P065? 0. S/DENEE Z4605 COOPER MM4 m 1965 J. COOPER ETAL 3,209,734

VAPOR GENERATOR WALL CONSTRUCTION Filed March 30, 1962 4 Sheets-Sheet 2 Oct. 5, 1965 .1. COOPER ETAL 3,209,734

VAPOR GENERATOR WALL CONSTRUCTION Filed March 50, 1962 4 Sheets-Sheet 5 W/ aw ATTORNEY Oct. 5, 1965 J. COOPER ETAL 3,209,734

VAPOR GENERATOR WALL CONSTRUCTION Filed March 30, 1962 H2 4 Sheets-Sheet 4 ATTOIP/Vf) United States Patent 3,209,734 VAPOR GENERATOR WALL CONSTRUCTION Jacob Cooper, Elmont, N.Y., and Roger I). Sidener, Westfield, N.J., assignors to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Mar. 30, 1962, Ser. No. 183,784 18 Claims. (Cl. 122-510) This invention relates to an improved wall construction and buckstay arrangement for a vapor generator, and particularly to a wall construction containing the heat absorbing elements and forming the combustion chamber and gas flow passages of the generator.

In modern vapor generators, the cold beam wall construction for the combustion chamber and gas flow passages is conventionally used, wherein the buckstays or annular retaining steel bands for the generator are disposed outside of the generator wall insulation.

For instance, in a typical generator having the walls of the combustion chamber and gas flow passages lined with banks or panels of liquid or vapor generating tubes for the absorption of heat, the tubes or tube panels will be encased by and will support a wall construction which may include a metal casing, insulation, a plurality of horizontal, retaining, buekstay rings and lagging.

The buckstays, in the form of I-beams, or other structural shapes, may completely encompass the generator engaging all four walls, and will be arranged to take or withstand lateral forces imposed on the wall by wind, internal pressure and other such forces. Channels underlying the buckstays are welded to the tubes and, the buckstays are supported on the channels through gussets and hooks. Between the buckstays, the tubes or heat absorbing components may be housed byjoined sections of flanged steel casing plates, which in turn are covered by one or more layers of insulation. The latter is arranged however, so that the buckstays are exposed to ambient temperature conditions.

In an alternative arrangement, for integral fin walls, basically the same wall construction is used except that no casing is required.

Because of the differential expansion or contraction between the tube panels and the buckstays during temperature changes in the generator, a compensating arrangement must be provided. The gussets and hooks permit a horizontal sliding movement between the buckstays and the supporting tubes, but additionally, the buckstays are usually tension tied at their ends to the adjacent generator walls by a pivotal linkage construction which permits a greater expansion or contraction of the tube panels within the encompassing buckstay ring.

This arrangement, however, has a number of disadvantages, one being that it is costly to make. Further, because the buckstays or beams are only pivotally connected at their ends, they deflect as simply supported beams when stressed by lateral forces such as pressure, puff or wind force, requiring a heavy gauge steel.

A further disadvantage of the construction is that close tolerances are required for the casing plates, principally because of the erection sequence required for the arrangement. The casing plates are positioned after location of the buckstays and end bars and must be cut to fit in place. This increases the expense in fabrication and shop time.

In the integral fin wall construction, the finned wall itself takes the tension in the generator walls. Since the strength of the wall thus depends on the strength of each tube, a serious limitation is placed on the design of any unit using this construction.

These and other disadvantages are overcome in accordance with the invention by providing in a vapor generator a wall in which the buckstays as well as the casing are exposed or subjected to tube temperatures. Specifical- 3,209,734 Fatented Oct. 5, 1965 ly, the generator wall, which comprises a plurality of substantially parallel tubes forming the generator tube panels, will have an array of adjacent, loose tolerance plates covering and secured to the outside of the tubes forming a skin casing for the generator. Preferably they are welded directly to the tubes. A framework including a plurality of substantially horizontal beams or buckstays is also secured to the tubes, and at least one layer of insulation is provided on the outside of the wall covering the tube, skin casing, and framework construction, maintaining the latter, including the buckstays, at substantially the same temperature as the tubes. In this way, the tube panels and the furnace wall including the buckstays will expand or contract at substantially the same rate and as a unitary structure.

In a preferred embodiment of the invention, the buckstays of adjacent walls of the generator are rigidly secured together at their ends, for instance by welding, to form a plurality of rigid, continuous, approximately horizontal bands encompassing the generator. The welded corner joints between buckstays, replacing the conventional, costly, expansion links or pin connections, may be tolerated since the tube panels, skin casing and buckstays maintain a substantially equal rate of growth.

The rigid frame construction of the buckstays stiifens them and reduces deflections and stresses in the beams when they are subjected to transverse forces. By so strengthening the buckstays, which for the purpose of this application, shall be termedmoment connecting-they may be made of a lighter weight material achieving a substantial saving in weight in the generator structure.

It will become apparent that the invention further facilitates fabrication of the generator wall, in eliminating the close tolerances heretofore required and simplifying the casing application. For instance, in one embodiment, the invention permits an erection sequence in which the casing plates are applied before the buckstays eliminating the need for close tolerance fits. Also the structure presents a more attractive over-all appearance in the unit.

A further understanding of the invention and other advantages thereof will become apparent upon consideration of the following detailed description, with reference to the accompanying drawings, in which:

FIG. 1 illustrates in section an elevation view of a steam generator embodying the concepts of the invention;

FIG. 2 is an enlarged fragmentary perspective View of a wall in the furnace portion of the generator of FIG. 1, in accordance with the invention;

FIG. 3 is an enlarged section view of a wall in the furnace portion of the generator taken along line 3-3 of FIG. 2;

FIG. 4 is a partial section view corresponding to that of FIG. 3 of an embodiment in accordance with the invention;

FIG. 5 is an enlarged section View of a gas flow passage of the generator taken along line 5-5 of FIG. 1;

FIG. 6 is an enlarged fragmentary section view of the furnace portion of the generator taken along line 6-6 of FIG. 1;

FIG. 7 is an enlarged section view corresponding to the view of FIG. 3 of a wall of a gas flow passage of the gen erator taken along line 7.+7 of FIG. 5;

FIG. 8 is a section view of a portion of the floor of the generator;

FIG. 9 is a section view taken along line 99 of FIG. 8;

FIG. 10 illustrates a wall construction for a fin Wall generator in accordance with the invention; and

FIG. 11 is a section view taken along line 1111 of FIG. 10.

Referring to FIG. 1, there is illustrated in section, an elevation view of a natural circulation oil fired steam generator with a welded pressurized casing. The generator is provided with a fluid cooled, combustion chamber 12 fired by burners 14 in the front wall 16 thereof, which combustion chamber is separated by a wall 18 from a plurality of adjacent water tubes defining a passage 20 for hot furnace gases. The passage 20 is divided by a baffle 22 into a first section 24 for down-flowing gases and a rising section 26 for upwardly flowing gases. The furnace is lined on all sides, with heat absorbing wall tubes in the gas passages as well as in the combustion chamber, and is lined along the roof and floor also. In the roof, the vapor liquid mixture is collected in a steam drum 28 and the liquid is returned by downcomers to a water drum 30 at the base of the generator.

The invention resides in the structure of the wall of the generator, both in the combustion chamber section and the hot furnace gas passages. Although the vapor generator illustrated in FIG. 1 is of relatively low capacity, the invention is useful on generators of many sizes and also for apparatus such as superheaters, economizers, and air heat exchangers where contraction and expansion as well as support of the components of the unit are a problem.

FIGS. 2, 3, 4 and 6 illustrate the wall construction of the furnace portion of the generator in accordance with the invention, and in particular the construction of the front wall 16. The tubes 32, which in this instance are contiguous to each other forming the front wall tube panel, extend in an approximately vertical direction and tie in with the steam drum 28 at the top of the generator.

A plurality of rectangular, casing plates 34 which are flanged or bent outwardly along a single horizontal edge (52, FIGS. 2 and 3), but flat along the remaining edges, are positioned adjacent to each other against the outside of the tube panel to form a skin casing for the furnace. The horizontal unflanged edges of the plates are welded directly to the tubes by weld points 36, FIG. 3, so that each plate is welded to every tube that it covers. As shown in FIG. 2, the plates are grouped in pairs so that flanged edges of the plates are brought together and the upper and lower unflanged edges of each pair are adjacent to but slightly spaced from unflanged edges of other pairs. The plates are dimensioned so as to provide a generous clearance or spacing (38, FIG. 2) in both the horizontal and vertical directions between the unflanged edges of the adjacent plates, to obviate the need for close tolerance shop or field work in the cutting of the plates. Also, where adjacent unflanged horizontal edges of pairs of vertically adjacent plates are welded to the tubes, the remaining plate edges, including the opposite horizontal flanged edges, are not welded to the tubes.

The horizontal buckstays, or I-beams 40, are then positioned so that their inner flanges cover the horizontal spacing between the pairs of plates and overlap the unflanged welded edges of vertically adjacent plates. They are then seal welded along edges 42 by their inner flanges directly to the outside surface of adjacetn plates sealing the casing wall at these points.

In a vertical direction, the spacing between horizontally adjacent plates 34 is covered or bridged by lap strips 44 seam welded along edges 46. Also in a vertical direction, the plates are provided with stilfening bars 48 stitch welded at spaced intervals, the bars being steel strips having a narrow edge welded to the outer surface of the plates, the strips extending outwardly from the plate surface. The outer flanges of the I-beams are supported by welding angle bars 50 between the outer flanges and the stiffening bars.

Between I-beams or buckstays, in a vertical direction the flanged edges 52 of pairs of the casing plates, as indicated, are brought together to form a V configuration. Disposed between the free ends of the plates, baflies or end bars 54 are located provided with a scalloped front or edge portion 56 conforming to and engaging the outer surfaces of adjacent tubes of the wall, the scalloped front or edge portion being seam welded to each tube. The baflle or end bars and casing plates are then seam welded along lines 58 to provide a gas tight structure.

The flange 52 permits a diiferential expansion or contraction in a vertical direction between the wall tubes 32 and the casing plates 34. By welding the end bars to the tubes, the differential expansion or contraction is taken up equally by each casing plate, while at the same time the free flanged edge of each plate is securely held against the tube bank. Also, the baffles or end bars 54 extend completely across the furnace in the space between the tubes and the casing plates 34 baflling the space at periodic intervals in a vertical direction to prevent the upward flow or racing of hot gases in this space, and overheating of the casing plates.

The outside of the wall construction is covered with insulation 60 so as to completely contain the above metal components including the buckstay or I-beam, as shown at 62, FIG. 3 providing a single ambient temperature for the components, approximately equal to the temperature of the tubes. The insulation may, for example, be composed of 2" to 3 thick blocks retained in place by conventional retaining clips 63, FIG. 2 disposed on the stiffening bars.

FIG. 6 illustrates the corner construction of a generator in accordance with the invention by which the buckstays or I-beams of adjacent walls are moment connected to each other. The I-beams are brought together so that the inside flange portion 64- of one of the I-beams overlaps the free end 66 of the other I-beam. They are initially fastened together by means of beam stops 68 and then are welded together at all points or lines of contact. stiffening plates '70 are added between flanges of the first beam, and are of the same thickness as the beam. All of the welds are full penetration welds. The tubes, casing plates and scalloped bars extend diagonally across the corner, and the corner area is sealed by triangular plates 72 welded to upper and lower flanges of the buckstays.

FIGURE 4 illustrates a modification wherein the edges 74 of adjacent casing plates 76 are bent outwardly and vertically to overlap and contact the outer edges of the inner flanges of the I-beams or buckstays 40. The

- I-beams, in this instance, are welded by stitch welds 78 directly to the wall tubes, and by seam welds 80 to the plates. Again, angle bars 50 are provided extending between the stiffening bars 48 and the outer flanges of the I-beams. In this embodiment, also, it is evident that the plates can be cut with loose tolerances, since the amount of overlap between the plates and I-beam flanges is not critical.

FIGS. 5 and 7 illustrates an arrangement suitable for use in a gas passage or heat recovery section of the generator, and for the rear wall of the generator. As illustrated in this figure, the tubes 82 are spaced apart and do not form a continuous water wall as in the furnace portion of the generator. However, the corner construction is the same, the beams of adjacent walls again being moment connected together.

The wide spaced tubes again are secured or aflixed to the buckstays 84, but preferably the buckstays are supported through Ts 86 the perpendicular portions 90 of which are welded to the tubes. In the embodiment illustrated, the cross portions 88 are field welded to the casing plates 92 which in turn are Welded to the buckstays. The arrangement described with respect to FIG. 4 can however be used.

As illustrated in FIG. 7, the Ts are shortened members having a length only slightly greater than the width of the flanges of the I-beam. Preferably they are provided with cut out areas 94 along the perpendicular edge welded to the tubes to avoid a rupture occurring because of a slight temperature differential between the welded components.

The wall in this section of the generator is also provided with end bars 96 between flanged edges of adjacent casing plates of the generator. These spaced bars are welded to the tubes by means of TS 98, as shown, but the end bars do not contact the tubes to provide a baflie and dead air space on the outside of tubes as with the arrangement of FIG. 3. Instead, a castable refractory 100, which may be poured in place or in the form of blocks, is disposed in the space between the tubes and the casing plates. If poured in, light weight stucco laths may be used welded between adjacent tubes to hold the refractory in position. Also, fins may be provided between the tubes defining a space with the casing plates into which the refractory is poured. The refractory is at or near the tube temperature during operation of the generator, so that the buckstay and easing structure also is substantially at the tube temperature.

In a typical wall construction for a low or medium capacity generator in accordance with any of the above concepts, the buckstays or I-beams may be located on 8 to 9 foot centers. The casing plates may have a No. ll

gauge thickness and will be stiffened by 2 x /4 inch stiffening bars on 26 inch centers. The entire construction will be covered with a 3 inch layer of insulation, and if desired, a No. 18 gauge insulation cover.

The principal advantages of the wall construction should now be evident. Most important is that the buckstays, casing and tube panels maintain a substantially equal rate of growth permitting the buckstays of adjacent walls to be moment connected together. By moment connecting all four corners, a plurality of rigid horizontal rings are provided encompassing the generator. The moment connection strengthens the buckstays, and a smaller web or span between beam flanges, as compared with simply supported beams, will suflice. This alone may represent about a 20% saving in weight in the generator structure.

Other advantages of the invention should also be apparent. For instance, moment connecting the buckstays together eliminates the complicated corner expansion joint conventionally required, further reducing the expense of the unit.

In erecting the generator, the tube panels are first erected, and the scalloped baffles 54, or the end bars 96 (FIG. 7), may then be located and welded to the tube panels. The casing or enclosure plates, to which the stiffening bars 48 have been aflixed, are then welded to the tubes, or the Ts as the case may be, and the buckstays are welded to the plates. In the FIGURE 4 embodiment, the sequence of the latter two steps may be reversed. The buckstays are initially supported by the stiffening bars 48 after which the corner joints are welded.

It is aparent that the erection sequence and procedure is considerably simplified. For instance, the step of first welding channels to the beams, and then gussets and hooks to the channels, is eliminated. But even more important, conventional units have required close tolerance plates flanged along both the upper and lower edges to fit between the prior positioned end bars and channels to which they are welded. By the invention, the need for close tolerances is eliminated as well as the flange along one edge of each plate.

FIGS. 8 and 9 illustrate a typical arrangement for the bottom wall or floor of the generator. The side wall tubes 32 of the generator are tied in with headers 104 on each side of the generator, the headers resting on foundations 106. The frame structure comprises a plurality of I-beams 108 welded to and extending between supports 110 which are seated on or across the tops of the headers 104, the I-beams extending in a transverse direction relative to the headers. The floor tubes 112 are supported by the I-beams, but are covered by easing plates 114 and insulation 116 in the same manner as for the wall tubes 32, FIG. 6. The plates are again stiffened by stiffening bars 118 and angle bars 120. End bars 122 are disposed between flanges 124 of adjacent plates,

6 and the floor construction is completed by placing floor tile 126 (FIG. 1) on and above the floor tubes.

FIGS. 10 and 11 illustrate a Wall construction in accordance with the invention for use with an integral fin tube panel, 130, FIG. 10. In the conventional units, the finned wall tube panel provides a gas tight structure and eliminates the need for a casing construction. Accordingly, the generator insulation is placed directly on the tubes. However, in other respects the wall construction is the same. welded to channels through gussets, the channels being welded to the tubes. The buckstays are outside of the insulation at ambient temperature, and must be corner connected by the expansion joints described above.

By the invention, the buckstays 132 are supported directly on the tubes and maintained at tube temperature by insulation 138 covering the buckstays as well as the tubes. One difference exists, however, in this embodiment of the invention. The tubes of the tube panel are wide spaced tubes connected by intermediate fins, and may expand or contract during start up or shut down at a rate slightly different from that of the buckstay. To avoid over stressing the tube panel and to permit a differential expansion, the buckstays are retained by upper and lower supporting hooks 134, welded to the tubes at points 136, and engaging the inner flanges of the buckstay. In addition, a generous. clearance 149 is provided between the hooks and the buckstay flanges equal to the expected differential growth between the finned generator wall and the hot buckstay ring. Despite the clearance, the buckstays will still supply center support for the tube panels so that deflection in a tube panel caused by lateral forces on the panel will substantially equal that in a buckstay.

The hot buckstay concept is particularly important with the integral finned wall, since, in conventional units, the tube panel takes all of the tension in the wall, imposing a serious limitation on its use. By the invention, tension in the wall is taken by the buckstay ring, permitting almost unlimited application of the integral finned wall construction.

Although the invention has been described with reference to specific embodiments, many modifications will be apparent to those skilled in the art, and the invention is to be limited as only defined in the following claims.

What is claimed is:

1. A vapor generator comprising;

at least two essentially flat connected vertically oriented walls at an angle of approximately with respect to each other, the walls defining an inner side and an outer side, the former coinciding with the 90 angle;

the walls comprising a plurality of substantially parallel continuous fin-tubes seam welded together providing a sealed casing for said chamber;

a framework for the walls comprising a plurality of essentially straight horizontal buckstays for each of the walls extending on said outer side in a direction transverse to the direction of the tubes;

the buckstays having a design adapted to withstand lateral forces imposed on the walls; the buckstays of one wall being moment connected directly to the finned tubes;

and at least one layer of insulation covering the fintubes and framework whereby the latter is maintained at substantially the same temperature as the tubes.

2. A vapor generator according to claim 1 wherein the buckstays are arranged to form a plurality of horizontal continuous bands encompassing the generator and engaging the walls of the generator, the buckstays of adjacent walls being moment connected together.

3. A vapor generator according to claim 2 further including spaced hooks welded to the casing tubes by which the buckstays are supported, said hooks being arranged to The buckstays are supported by hooks Y provide a lateral clearance permitting a differential expansion of the generator within the encompassing buckstay rings.

4. A vapor generator comprising;

at least two essentially fiat connected walls at an angle of approximately 90 with respect to each other, the walls defining an inner side and an outer side, the former coinciding with the 90 angle;

said walls comprising a plurality of substantially parallel vertically oriented adjacent tubes, means integral with the tubes sealing the tubes so that the walls are substantially gas tight;

a framework for the walls comprising a plurality of essentially straight horizontal buckstays on said outer side extending in a direction transverse to the direction of the tubes;

the buckstays having a design adapted to withstand lateral forces imposed on the walls; the buckstays of one wall being moment connected to those of the other adjacent the line of contact between the walls so that the framework is rigid;

the buckstays being rigidly weld connected directly to the walls;

at least one layer of insulation covering the walls and framework arranged to maintain the buckstays at substantially the same temperature as the tubes.

5. A vapor generator comprising;

opposed vertical essentially flat connected walls defining a rectangular chamber, the walls having an inner side and an outer side;

said walls comprising a plurality of substantially parallel adjacent tubes;

a plurality of loose tolerance casing plates in approximately abutting relationship covering the outer side of the tubes welded to the tubes to form a skin casing for said chamber;

a framework for the walls comprising a plurality of spaced-apart essentially straight horizontal buckstays seam welded to the casing plates so as to cover the spacing between adjacent plates;

the buckstays having a design adapted to withstand lateral forces imposed on the walls;

the buckstays of one wall being moment connected to those of another adjacent the line of contact between the walls so that the framework is rigid to form a plurality of horizontal rigid bands encompassing the chamber;

at least one layer of insulation covering the walls and framework arranged to maintain the buckstays at substantially the same temperature as the tubes.

6. A vapor generator according to claim wherein the buckstays are I-beams, the inner flanges of which are super-imposed with and seal welded to the edge portions of adjacent casing plates across the spacing between the plates, by which the casing plates may be cut with loose tolerances for positioning against the tubes.

7. A vapor generator according to claim 6 wherein the casing plates are secured directly to the tubes only along a single horizontal edge superimposed with a buckstay, said skin casing further including expansion joints through which the opposite horizontal edge of said plates is welded to an adjacent plate.

8. A vapor generator according to claim 7 wherein the expansion joint includes an elongated, flat end bar disposed between the adjacent plates and welded to the tubes of the wall, the plates having flexible edge portions seal welded to opposite sides of the end bar so that the differential expansion between the tubes and the plates in a vertical direction is taken up equally by each plate.

9. A vapor generator according to claim 8 wherein said flexible edge portions are longitudinal flanges extending outwardly and towards th adjacent plate to form a V-configuration with the interposed end bar, the configuration providing for differential expansion between the tubes and the plates.

10. A vapor generator according to claim 5 wherein the tubes are spaced apart from each other, the wall further including elongated Ts extending between and welded to the casing plates and tubes spacing the tubes from the surface of the plates, the cross-portions of the Ts being welded to the plates and the base portions of the Ts being welded to the tubes.

11. A vapor generator according to claim 10 including a layer of refractory material disposed in the space between the tubes and the casing plates.

12. A vapor generator comprising:

opposed vertical essentially flat connected walls defining an upright enclosed rectangular chamber, the walls having an inner side and an outer side;

said walls comprising a plurality of substantially parallel vertically oriented adjacent tubes;

a plurality of loose tolerance, rectangular casing plates in approximately abutting relationship covering the outer side of the tubes welded to the tubes to form a skin casing for said chamber, pairs of said vertically adjacent plates having adjacent horizontal edges secured to the tube;

a plurality of expansion joints, the opposite horizontal edges of said pairs of plates being seal welded to the next vertically adjacent plates through said expansion joints;

a framework for the walls comprising a plurality of spaced-apart essentially straight horizontal buckstays having inner flanges superimposed with and seam welded to the secured edges of pairs of plates to cover the spacing between the plates, the buckstays extending on the outer side of said walls in a direction transverse to the direction of the tubes;

the buckstays having a design adapted to withstand lateral forces imposed on the walls;

the buckstays of one wall being moment connected to those of another adjacent the line of contact between the walls forming a plurality of annular continuous. rigid bands which encompass the chamber;

at least one layer of insulation covering the walls and framework arranged to maintain the buckstays at substantially the same temperature as the tubes.

13. A vapor generator according to claim 12 and further including a plurality of horizontal end bars disposed along said expansion joints between adjacent plates and rigidly secured to the tubes, the plates having flanged portions seal welded to opposite sides of the bars, the differential expansion between the tubes and plates in a vertical direction being taken up by each plate.

14. A vapor generator according to claim 12 wherein the generator is provided with four walls at right angles to each other, the buckstays being I-beams rigidly connected together at right angles to each other to form a plurality of rigid, continuous approximately horizontal bands encompassing the generator.

15. A vapor generator according to claim 14 wherein the casing plates are welded directly to the tubes along said superimposed edge portions and the buckstay inner flanges are seal welded to the outside of the plates.

16. A vapor generator according to claim 14 wherein the I-beams are Welded directly to the tubes and the casing plates are formed along their superimposed edge portions to overlap and engage the outside surfaces of the inner flanges of the I-beams to which they are welded.

17. A vapor generator comprising:

opposed essentially flat vertically oriented connected walls defining an upright enclosed rectangular chamber, the walls having an inner side and an outer side;

said walls comprising a plurality of substantially parallel vertically oriented adjacent tubes;

a plurality of loose tolerance rectangular casing plates in approximately abutting relationship covering the outer side of the tubes welded to the tubes to form a skin casing for said chamber, vertically adjacent plates being paired and comprising an expansion 9 1% joint connecting and sealing the pairs of plates along and framework arranged to maintain the buckstays adjacent edges; at substantially the same temperature as the tubes. said plates being cut with wide tolerances to provide a 18. A wall construction according to claim 17 and spacing between uppermost and lowermost edges of further including spaced vertically oriented stiffening bars the pairs, said pairs of vertically adjacent plates hav- 5 Welded to the outside surface of each casing plate, and ing uppermost and lowermost edges secured to the retaining clips Welded to said bars by which said insulatubes; tion is retained on the surface of the generator. a framework for the walls comprising a plurality of essentially straight horizontal spaced-apart buckstays References Cited y the Examiner fodr each ofdthetwallst extendingtonfitlhedwalls outerf" 10 UNITED STATES PATENTS f i g f ransverse 6 0 1,761,567 6/30 Kerr l22- 6 said buckstays having an I-beam design adapted to girdgrove et a1 5 58 withstand lateral forces imposed on the walls, ar- 2703559 3/55 5 g g 3 ranged so that their inner flanges are superimposed 2773487 12/56 a 122494 with and seam welded to opposite secured edges of 287O750 1/59 i gi gg a 7 X afg gfi g of plates to the spacmg between 2,920j609 1/60 Iager, et al 122 240 the buckstays of one wall being rigidly moment con- Rurham nected to those of adjacent walls adjacent the lines 30O7455 11/61 f 122-6 of contact between the walls forming a plurality of 3O30937 4/62 wi 122 6 1 J substantlal y horizontal, rigid continuous bands 3,046,957 7/62 Witzke 122*510 around the walls;

a plurality of lap strips vertically disposed and welded to the plates to Cover and Seal the Vertical p g r FREDERICK L. MATTESON, JR., Przmary Exammer.

2 between the adjacent plates; 0 PERCY L. PATRICK, MEYER PERLIN, KENNETH and at least one layer of insulation covering the walls W. SPRAGUE, Examiners. 

1. A VAPOR GENERATOR COMPRISING: AT LEAST TWO ESSENTIALLY FLAT CONNECTED VERTICALLY ORIENTED WALL AT AN ANGLE OF APPROXIMATELY 90* WITH RESPECT TO EACH OTHER, THE WALLS DEFINING AN INNER SIDE AND AN OUTER SIDE, THE FORMER COINCIDING WITH THE 90* ANGLE; THE WALL COMPRISING A PLURALITY OF SUBSTANTIALLY PARALLEL CONTINUOUS FIN-TUBES SEAM WELDED TOGETHER PROVIDING A SEALED CASING FOR SAID CHAMBER; A FRAMEWORK FOR THE WALLS COMPRISING A PLURALITY OF ESSENTIALLY STRAIGHT HORIZONTAL BUCKSTAYS FOR EACH OF THE WALLS EXTENDING ON SAID OUTER SIDE IN A DIRECTION TRANSVERSE TO THE DIRECTION OF THE TUBES; THE BUSKSTAYS HAVING A DESIGN ADAPTED TO WITHSTAND LATERAL FORCES IMPOSED ON THE WALLS; THE BUSKSTAYS OF ONE WALL BEING MOMENT CONNECTED DIRECTLY TO THE FINNED TUBES; AND AT LEAST ONE LAYER OF INSULATION COVERING THE FINTUBES AND FRAMEWORK WHEREBY THE LATTER IS MAINTAINED AT SUBSTANTIALLY THE SAME TEMPERATURE AS THE TUBES. 